There is a known technique in which a plurality of storage apparatuses are clustered so that, if one of the clustered storage apparatuses stops due to a failure or another problem, another storage apparatus takes over its role. For example, two storage apparatuses are clustered, and the data stored in a storage area of one active storage apparatus, which is accessed from a host device, is copied to a storage area of the other standby storage apparatus so as to synchronize these storage areas. Then, if the active storage apparatus stops, a storage area to be accessed from the host device is changed to the storage area of the other storage apparatus, so as to allow the host device to keep on performing its tasks.
In addition, there is proposed a technique in which the data stored in a storage area of one storage apparatus is copied to a storage area of another storage apparatus, and further the data stored in the copy destination storage area is copied to another storage area within the other storage apparatus. There is also proposed a technique in which, in addition to the above copies, the data stored in the copy source storage area is copied to another storage area within the one storage apparatus.
Please see, for example, Japanese Laid-open Patent Publications Nos. 2003-233518 and 2010-39986.
One of systems employing the above techniques in which storage apparatuses are clustered is as follows. A first storage apparatus having first and second storage areas and a second storage apparatus having third and fourth storage areas are clustered. The first storage apparatus, while in active state, backs up the data stored in the first storage area, which is accessed from a host device, to the second storage area. In addition, the data stored in the first storage area is copied to the third storage area, and the data stored in the second storage area is copied to the fourth storage area, in order that data is synchronized between copy source and copy destination storage areas.
In the system as described above, when the first storage apparatus stops and the third storage area starts to get accessed from a host device, the fourth storage area already contains a backup of the data stored in the third storage area. Therefore, a failover is performed without losing data redundancy.
However, in order to back up the data stored in the third storage area to the fourth storage area after a failover, an administrator needs to make some settings to execute the backup. Therefore, it takes time to back up the data of the third storage area to thereby ensure the safety of the data after the host device starts to update the data in the third storage area.